Scale effects on fluid flow and heat transfer in microchannels

Many investigators have recently experimentally established that fluid flow and heat transfer characteristics in microchannels, used to cool electronic chips, deviate from those of normally sized channels. Deviations increase as the channel size decreases. Many hypotheses were advanced to explain some of the observed deviations. However, they were usually in contradiction with other observed deviations. Hence, no conclusive explanation has been given so far for these phenomena. In this work, observed deviations will be listed, different hypotheses advanced to interpret these deviations will he critically revised. Finally, a new hypothesis will be advanced based on the increased role of surface roughness on flow and heat transfer in microchannels. Simple models will be built capable of reproducing observed trends for both friction and heat transfer coefficient in the laminar region, as well as giving an improved prediction for the laminar turbulent transition.